Abstract:

Beet leafhoppers were collected weekly on
yellow sticky traps placed at 36 locations in Morrow and
Umatilla Counties in northeastern Oregon in April through
November 2007, 2008, and 2009. Insects were counted,
collected, and a subset of the insects was tested for the
presence of the beet leafhopper-transmitted virescence
agent phytoplasma, the causal agent of potato purple top
disease in this region. Beet leafhoppers were present
throughout the sampling period and the number of insects
collected peaked in June of each year with smaller peaks in
July and October. Of the 804 insects tested for phytoplasma
in 2007, 2008, and 2009, 21, 18, and 22% tested positive
for phytoplasma, respectively. Most of the phytoplasma-positive
insects were collected from mid-June through July.
Positive insects, however, were collected as late as 13
November in 2007 and 2008. These data indicate that a
relatively high proportion of the beet leafhoppers in this
area are harboring the phytoplasma. Therefore, the potential
for development of purple top disease of potatoes from
migrating beet leafhoppers in this important potato producing
region is quite high and measures to control this pest
throughout the growing season are probably necessary in
order to reduce disease pressure.